Conventionally, in general, soundproof wall equipment merely has the soundproof panels arranged in plural stages in the vertical direction, and acoustic materials provided in the acoustic spaces of these soundproof panels are materials having the same acoustic performance with a constant surface density. A sound-source-side front surface portion of each soundproof panel is formed to be a sound transmitting surface, while each soundproof panel has, on the back surface side thereof, a sound insulating surface formed of a rigid plate, to achieve a sound insulating wall function (for example, see Patent Literature 1).
Therefore, there is a great sound pressure difference between the sound source side and the back surface side of the soundproof panels arranged in the vertical direction, and in the vicinity of the upper end edge of the soundproof wall equipment, the energy of accelerated sound (this is referred to as “edge effect”) causes a diffraction phenomenon, resulting in a problem that the diffracted sound spreads toward the residential area on the back surface side of the soundproof wall equipment.
Accordingly, in order to solve the above problem, technology referred to as “edge effect suppression technology” is proposed in which a sound absorbing panel having sound transmitting surfaces formed in a sound-source-side front surface portion and a back surface portion is provided further above the uppermost one of the soundproof panels arranged in plural stages in the vertical direction, thereby enabling reduction in the diffraction sound that is to be diffracted in the vicinity of the upper end edge of the uppermost one of the soundproof panels arranged in plural stages in the vertical direction (for example, see Patent Literature 2).